Hey alexios225,
It is possible that contacts you message may not have read receipts enabled on their device, as that is a setting on the receivers end, there would not be an option for you to adjust that.
You can learn more about that here:
"iMessage read receipts let iMessage users know when their messages have been read. With read receipts on, the person who sent you the iMessage gets a Read indicator below the message after you’ve read it. With read receipts off, they see only that the message has been delivered.
You have the option to send read receipts for all conversations, or only for individual ones. If you’ve turned on read receipts for all conversations, you can still turn them off for individual ones—and vice versa.
Note: Read receipts aren’t supported with SMS messaging and with group texts.
- On your iPhone or iPad: Go to Settings > Messages, then turn Read Receipts on or off.
- On your Mac running macOS Ventura 13 or later: Open Messages go to Messages > Settings, click the iMessage tab, then select or deselect Send Read Receipts.
- On your Mac running macOS 12 or earlier: Open Messages go to Messages > Preferences, click the iMessage tab, then select or deselect Send Read Receipts."
Thanks!